Better known by trade names such as Symmetrel, Gocovri and Osmolex ER, amantadine was initially used as an antiviral medication in people. Currently, it’s being prescribed “off label” to offer strong pain relief for dogs.
“The FDA allows veterinarians to prescribe approved human and animal drugs for extra-label uses in animals under specific conditions,” explains Dr. Chad Maki of Huntington Beach, California. “A particular drug that is not approved for a certain condition may be prescribed by a veterinarian for the aforementioned condition as long as it meets specific criteria.”
The veterinarian’s direction for use may be significantly different from those on the label – hence the term “off-label.”
Typically, amantadine is prescribed in conjunction with other medications to offer strong pain relief for dogs from osteoarthritis, tendonitis, spine/disc pain, pain from tumors/cancer, neuropathic pain and other chronic pain. It’s used as an anti-hyperalgesic (not an analgesic). This works on the brain to help reduce central sensitization, a condition where there is over-amplification of pain signals.
“It is ineffective when used alone and must be used with other true analgesics, such as non-steroidal anti-inflammatories, gabapentin, opioids,” explains Dr. Maki.
“Amantadine is given at 3 to 5 mg/kg by mouth twice daily in the form of a capsule, tablet or liquid solution,” says Dr. Maki. “It can be given with or without food, but if your pet vomits after receiving the medication on an empty stomach, try giving it with a small meal or treat. And, be patient,” he adds. “It can take 21 days or longer before the full effect can be appreciated.”
Amantadine is excreted by the kidneys, so dogs with kidney disease need careful monitoring and may be on a lower dose as a caution.
“Further, there are important drug interactions to consider,” cautions Dr. Maki, “such as prescribing the drug with antihistamines like Benadryl as this has been known to exacerbate the anticholinergic effects of both drugs, which include dry mouth expressed with excessive thirst and excessive lip smacking, difficulty urinating and rapid heart rate. It also needs careful monitoring when given together with an anti-anxiety medication like clomipramine (Clomicalm).”
The use of amantadine with tramadol, a common pain medication for dogs, may increase the risk of seizures.
Because experience with this drug is still limited, it’s still a learning curve for veterinarians. However, possible side effects of amantadine in dogs include:
At toxic doses, side effects include tremors, anxiety, incoordination and increased salivation and vomiting.
However, because it’s a new drug to veterinary medicine, there are currently no known dependencies or addictions to this medication. There are no age restrictions for this drug to be prescribed. However, most cases of “chronic pain” target older dogs.